This invention relates generally to keyswitch activated displays and particularly to displays including keyswitches in which interruption of a beam of radiant energy generates an electrical signal. Still more particularly, this invention relates to a keyswitch activated display including an optical keyswitch responsive to the touch of an operator's finger or a stylus to display alphanumeric or graphic characters.
Keyswitch activated displays are used with electronic systems for displaying legends selected by an operator. The display implements interaction between the operator and the system so that the operator may ascertain that a selected operational feature of the system was activated in response to a touch on the keyswitch.
A touch input device typically has a relatively flat screen or plate with a space in front of the screen being traversed by one or more beams of radiant energy. The radiant energy generally defines a line or a plane parallel to the surface of the screen. Interruption of the radiant energy flow is detected to form an electrical signal indicative of the location of the point where the screen has been touched. Typically, an infrared light source such as a light emitting diode (LED) produces the radiant energy in the form of a beam of infrared light. Phototransistors or other infrared detectors detect the infrared light beam.
The LEDs and phototransistors are often used in a touch panel with the LEDs being mounted along one side and the phototransistors being mounted along the opposite edge. The usual arrangement thus has the light sources and light detectors coplanar with or nearly coplanar with the plane of the keypad. The typical structure requires electrical circuitry in the plane of the touch panel, which adds to the complexity and area of such devices.
U.S. Pat. No. 4,467,193 to Carroll discloses a parabolic light emitter and detector unit including a solid state light emitter embedded in a transparent body formed with one planar surface and an opposing surface formed as a paraboloid. The outer surface of the paraboloid is coated with a light reflecting material to form a mirror. The light emitter is located at the focus of the paraboloid so that light reflecting therefrom forms a parallel beam.
U.S. Pat. No. 4,384,201 and U.S. Pat. No. 4,267,443 to Carroll et al. disclose a three dimensional protective interlock apparatus that includes a photoelectric touch panel. The photoelectric touch panel has a first pair of crossed light beams that define a first plane. When the beams are broken by an object, the panel provides signals indicative of the coordinates of the object in the plane. A second pair of crossed light beams define a second plane, and the relationship between the beams in the two planes is employed to distinguish between objects that interrupt the beams based upon the size, spatial orientation and velocity. The number of beams broken in the planes are counted to determine the size of the interrupting object.
U.S. Pat. No. 4,306,147 to Fukuyama et al discloses a photoelectric switching apparatus having a light projecting device and a light detecting device mounted such that the output beam of the light projecting device crosses the region from which a light beam can impinge upon the detector and produce a response. Light from the projecting device normally is not incident upon the detector except when an object interrupts the beam at a location where light reflected from the object impinges upon the detector.
U.S. Pat. No. to Bergstrom discloses an optoelectronic circuit element for effecting an manually controlled output signal. The optoelectronic circuit element includes an LED that directs a light beam into a glass prism such that the beam totally internally reflects at an interface toward a detector. The amount of light reflected to the detector is decreased when the finger of an operator contacts the prism at the point of reflection. The finger is an absorbing medium that interacts with the evanescent portion of the beam to couple energy therefrom. Decreasing the intensity of the light incident upon the detector produces an electrical signal.
U.S. Pat. No. 4,243,879 to Carroll et al. discloses a touch panel that includes apparatus for sampling the ambient light immediately before a pulse of radiant energy is transmitted to a photoelectric transducer. The output of the photoelectric transducer is compared with the output during the previous ambient interval to develop a signal indicative of the presence or absence of the pulse irrespective of ambient light fluctuations.
U.S. Pat. No. 3,862,415 to Harnden, Jr. et al. discloses an optoelectronic object detector using a semiconductor light source. The light source and a photosensitive device are positioned on a single header member with an optical barrier therebetween. Light emitted by the light source is reflected from an object in the path of the light, and impinges upon the detector. The barrier prevents the light source from directly illuminating the detector.
U.S. Pat. No. 3,906,222 to Astler et al. is directed to an electrical push button switch with photoelectrical switching elements. The push button is slidably supported in a casing, and a return spring acts on the push button to urge it to a raised position away from the casing. The casing includes two hollow portions facing one another and formed of transparent material, a light source in one hollow portion and a photoelectric element in the other hollow portion. the push button carries a screen for blocking communication between the light source and the photoelectric element when the push button is depressed to an operative position.
U.S. Pat. No. 3,851,328 to Sottile et al. discloses an optical solid state switch for use in a control panel. A light emitting diode is embedded in one side of the panel, and a photodetector is is embedded in the other side so that an operator may place his finger in the opening to obtain a switching action. Logic circuits and display devices may be added to the switch to permit it to be used as an alternate action switch, potentiometer, rotary switch and thumbwheel apparatus. A multiplexing apparatus is included in applications where a large number of these devices are installed on a control panel.